MindMup is a free, easy to use mind mapping tool. It plugs into Google Drive too, so it is easy to save and recall them for later use. It is possible to set up MindMup for collaborative use as well, making it a great tool for group work. Finished mups..er maps.. can be exported as PDF's. There are tons of mind mapping mapping tools out there and a good few that are online, but not all of them are as easy to use and accessible as MindMup.